Coils for generating a plasma and for sputtering

ABSTRACT

A sputtering coil for a plasma chamber in a semiconductor fabrication system is provided. The sputtering coil couples energy into a plasma and also provides a source of sputtering material to be sputtered onto a workpiece from the coil to supplement material being sputtered from a target onto the workpiece. Alternatively a plurality of coils may be provided, one primarily for coupling energy into the plasma and the other primarily for providing a supplemental source of sputtering material to be sputtered on the workpiece.

RELATED APPLICATIONS

This application is a continuation of application Ser. No. 08/851,946entitled “Coils for Generating a Plasma and for Sputtering.” filed May6, 1997, now U.S. Pat No. 6,368,469 which is a continuation ofapplication Ser. No. 08/680,335 filed Jul. 10, 1996, abandoned which isa continuation-in-part of application Ser. No. 08/644,096 entitled“Coils for Generating a Plasma and for Sputtering,” filed May 10, 1996,abandoned which is a continuation-in-part of copending application Ser.No. 08/647,184 entitled “Sputtering coil for Generating a Plasma,” filedMay 9, 1996 abandoned.

FIELD OF THE INVENTION

The present invention relates to plasma generators, and moreparticularly, to a method and apparatus for generating a plasma tosputter deposit a layer of material in the fabrication of semiconductordevices.

BACKGROUND OF THE INVENTION

Low pressure radio frequency (RF) generated plasmas have becomeconvenient sources of energetic ions and activated atoms which can beemployed in a variety of semiconductor device fabrication processesincluding surface treatments, depositions, and etching processes. Forexample, to deposit materials onto a semiconductor wafer using a sputterdeposition process, a plasma is produced in the vicinity of a sputtertarget material which is negatively biased. Ions created within theplasma impact the surface of the target to dislodge, i.e., “sputter”material from the target. The sputtered materials are then transportedand deposited on the surface of the semiconductor wafer.

Sputtered material has a tendency to travel in straight line paths fromthe target to the substrate being deposited at angles which are obliqueto the surface of the substrate. As a consequence, materials depositedin etched trenches and holes of semiconductor devices having trenches orholes with a high depth to width aspect ratio, can bridge over causingundesirable cavities in the deposition layer. To prevent such cavities,the sputtered material can be redirected into substantially verticalpaths between the target and the substrate by negatively charging thesubstrate and positioning appropriate vertically oriented electricfields adjacent the substrate if the sputtered material is sufficientlyionized by the plasma. However, material sputtered by a low densityplasma often has an ionization degree of less than 1% which is usuallyinsufficient to avoid the formation of an excessive number of cavities.Accordingly, it is desirable to increase the density of the plasma toincrease the ionization rate of the sputtered material in order todecrease the formation of unwanted cavities in the deposition layer. Asused herein, the term “dense plasma” is intended to refer to one thathas a high electron and ion density.

There are several known techniques for exciting a plasma with RF fieldsincluding capacitive coupling, inductive coupling and wave heating. In astandard inductively coupled plasma (ICP) generator, RF current passingthrough a coil surrounding the plasma induces electromagnetic currentsin the plasma. These currents heat the conducting plasma by ohmicheating, so that it is sustained in steady state. As shown in U.S. Pat.No. 4,362,632, for example, current through a coil is supplied by an RFgenerator coupled to the coil through an impedance matching network,such that the coil acts as the first windings of a transformer. Theplasma acts as a single turn second winding of a transformer.

In many high density plasma applications, it is preferable for thechamber to be operated at a relatively high pressure so that thefrequency of collisions between the plasma ions and the depositionmaterial atoms is increased to increase thereby the resident time of thesputtered material in the high density plasma zone. However, scatteringof the deposition atoms is likewise increased. This scattering of thedeposition atoms typically causes the thickness of the deposition layeron the substrate to be thicker on that portion of the substrate alignedwith the center of the target and thinner in the outlying regions. Ithas been found that the deposition layer can be made more uniform byreducing the distance between the target and the substrate which reducesthe effect of the plasma scattering.

On the other hand, in order to increase the ionization of the plasma toincrease the sputtering rate and the ionization of the sputtered atoms,it has been found desirable to increase the distance between the targetand the substrate. The coil which is used to couple energy into theplasma typically encircles the space between the target and thesubstrate. If the target is positioned too closely to the substrate, theionization of the plasma can be adversely affected. Thus, in order toaccommodate the coil which is coupling RF energy into the plasma, it hasoften been found necessary to space the target from the substrate acertain minimum distance even though such a minimum spacing can have anadverse effect on the uniformity of the deposition.

SUMMARY OF THE PREFERRED EMBODIMENTS

It is an object of the present invention to provide an improved methodand apparatus for generating a plasma within a chamber and for sputterdepositing a layer which obviate, for practical purposes, theabove-mentioned limitations.

These and other objects and advantages are achieved by, in accordancewith one aspect of the invention, a plasma generating apparatus whichinductively couples electromagnetic energy from a coil which is alsoadapted to sputter material from the coil onto the workpiece tosupplement the material being sputtered from a target onto theworkpiece. The coil is preferably made of the same type of material asthe target so that the atoms sputtered from the coil combine with theatoms sputtered from the target to form a layer of the desired type ofmaterial. It has been found that the distribution of material sputteredfrom a coil in accordance with one embodiment of the present inventiontends to be thicker at the edges of the substrate and thinner toward thecenter of the substrate. Such a distribution is very advantageous forcompensating for the distribution profile of material sputtered from atarget in which the material from the target tends to deposit morethickly in the center of the substrate as compared to the edges. As aconsequence, the materials deposited from both the coil and the targetcan combine to form a layer of relatively uniform thickness from thecenter of the substrate to its edges.

In one embodiment, both the target and the coil are formed fromrelatively pure titanium so that the material sputtered onto thesubstrate from both the target and the coil is substantially the samematerial, that is, titanium. In other embodiments, other types ofmaterials may be deposited such as aluminum. In which case, the coil aswell as the target would be made from the same grade of aluminum, i.e.,target grade aluminum. In other embodiments the target can be made of amaterial such as Cr, Te or SiO₂. If it is desired to deposit a mixtureor combination of materials, the target and the coil can be formed fromthe same mixture of materials or alternatively from different materialssuch that the materials combine or mix when deposited on the substrate.

In yet another embodiment, a second coil-like structure in addition tothe first coil, provides a supplemental target for sputtering material.This second coil is preferably not coupled to an RF generator but isinstead biased with DC power. Although material may or may not continueto be sputtered from the first coil, sputtered material from the coilswill originate primarily from the second coil because of its DC biasing.Such an arrangement permits the ratio of the DC bias of the primarytarget to the DC bias of the second coil to be set to optimizecompensation for non-uniformity in thickness of the material beingdeposited from the primary target. In addition, the RF power applied tothe first coil can be set independently of the biases applied to thetarget and the second coil for optimization of the plasma density forionization.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective, partial cross-sectional view of a plasmagenerating chamber in accordance with one embodiment of the presentinvention.

FIG. 2 is a schematic diagram of the electrical interconnections to theplasma generating chamber of FIG. 1.

FIG. 3 is a perspective view of a coil ring for a plasma generatingapparatus in accordance with another embodiment of the presentinvention.

FIG. 4 is a schematic partial cross-sectional view of a plasmagenerating chamber in accordance with another embodiment of the presentinvention utilizing a coil ring as shown in FIG. 3.

FIG. 5 illustrates a plurality of coil ring support standoffs for theplasma generating chamber of FIG. 4.

FIG. 6 illustrates a plurality of coil ring feedthrough standoffs forthe plasma generating chamber of FIG. 4.

FIG. 7 is a chart depicting the respective deposition profiles formaterial deposited from the coil and the target of the apparatus of FIG.1.

FIG. 8 is a graph depicting the effect on deposition uniformity of theratio of the RF power applied to the coil relative to the DC power biasof the target.

FIG. 9 is a schematic partial cross-sectional view of a plasmagenerating chamber in accordance with another embodiment of the presentinvention utilizing dual coils, one of which is RF powered for plasmageneration and the other of which is DC biased to provide a supplementaltarget.

FIG. 10 is a schematic diagram of the electrical interconnections to theplasma generating chamber of FIG. 10.

FIG. 11 illustrates a plurality of coil ring feedthrough standoffs for aplasma generating chamber having two multiple ring coils in which therings of the two coils are interleaved.

FIG. 12 is a schematic diagram of the electrical interconnections to theplasma generating chamber of FIG. 11.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring first to FIGS. 1 and 2, a plasma generator in accordance witha first embodiment of the present invention comprises a substantiallycylindrical plasma chamber 100 which is received in a vacuum chamber 102(shown schematically in FIG. 2). The plasma chamber 100 of thisembodiment has a single turn coil 104 which is carried internally by ashield 106. The shield 106 protects the interior walls (not shown) ofthe vacuum chamber 102 from the material being deposited within theinterior of the plasma chamber 100.

Radio frequency (RF) energy from an RF generator 106 is radiated fromthe coil 104 into the interior of the deposition system 100, whichenergizes a plasma within the deposition system 100. The energizedplasma produces a plasma ion flux which strikes a negatively biasedtarget 110 positioned at the top of the chamber 102. The target 110 isnegatively biased by a DC power source 111. The plasma ions ejectmaterial from the target 110 onto a substrate 112 which may be a waferor other workpiece which is supported by a pedestal 114 at the bottom ofthe deposition system 100. A rotating magnet assembly 116 provided abovethe target 110 produces magnetic fields which sweep over the face of thetarget 110 to promote uniform erosion of the target.

The atoms of material ejected from the target 110 are in turn ionized bythe plasma being energized by the coil 104 which is inductively coupledto the plasma. The RF generator 106 is preferably coupled to the coil104 through an amplifier and impedance matching network 118. The otherend of the coil 104 is coupled to ground, preferably through a capacitor120 which may be a variable capacitor. The ionized deposition materialis attracted to the substrate 112 and forms a deposition layer thereon.The pedestal 114 may be negatively biased by an AC (or DC or RF) source121 so as to externally bias the substrate 112. As set forth in greaterdetail in copending application Ser. No. 08/677,588, filed Jul. 9, 1996,Express Mail Certificate No. EM 129 431 588, entitled “Method forProviding Full-Face High Density Plasma Deposition” by Ken Ngan, SimonHui and Gongda Yao, which is assigned to the assignee of the presentapplication and is incorporated herein by reference in its entirety,external biasing of the substrate 112 may optionally be eliminated.

As will be explained in greater detail below, in accordance with oneaspect of the present invention, material is also sputtered from thecoil 104 onto the substrate 112 to supplement the material which isbeing sputtered from the target 110 onto the workpiece. As a result, thelayer deposited onto the substrate 112 is formed from material from boththe coil 104 and the target 110 which can substantially improve theuniformity of the resultant layer.

The coil 104 is carried on the shield 106 by a plurality of coilstandoffs 122 (FIG. 1) which electrically insulate the coil 104 from thesupporting shield 106. As set forth in greater detail in copendingapplication Ser. No. 08/647,182, entitled Recessed Coil for Generating aPlasma, filed May 9, 1996 (Attorney Docket #1186/PVD/DV) and assigned tothe assignee of the present application, which application isincorporated herein by reference in its entirety, the insulating coilstandoffs 122 have an internal labyrinth structure which permitsrepeated deposition of conductive materials from the target 110 onto thecoil standoffs 122 while preventing the formation of a completeconducting path of deposited material from the coil 104 to the shield106 which could short the coil 104 to the shield 106 (which is typicallyat ground).

RF power is applied to the coil 104 by feedthroughs (not shown) whichare supported by insulating feedthrough standoffs 124. The feedthroughstandoffs 124, like the coil support standoffs 122, permit repeateddeposition of conductive material from the target onto the feedthroughstandoff 124 without the formation of a conducting path which couldshort the coil 104 to the shield 106. Thus, the coil feedthroughstandoff 124 has an internal labyrinth structure somewhat similar tothat of the coil standoff 122 to prevent the formation of a shortbetween the coil 104 and the wall 140 of the shield.

As best seen in FIG. 1, the plasma chamber 100 has a dark space shieldring 130 which provides a ground plane with respect to the target 110above which is negatively biased. In addition, as explained in greaterdetail in the aforementioned copending application Ser. No. 08/647,182,the shield ring 130 shields the outer edges of the target from theplasma to reduce sputtering of the target outer edges. The dark spaceshield 130 performs yet another function in that it is positioned toshield the coil 104 (and the coil support standoffs 122 and feedthroughstandoffs 124) from the material being sputtered from the target 110.The dark space shield 130 does not completely shield the coil 104 andits associated supporting structure from all of the material beingsputtered since some of the sputtered material travels at an obliqueangle with respect to the vertical axis of the plasma chamber 100.However, because much of the sputtered material does travel parallel tothe vertical axis of the chamber or at relatively small oblique anglesrelative to the vertical axis, the dark space shield 130 which ispositioned in an overlapping fashion above the coil 104, prevents asubstantial amount of sputtered material from being deposited on thecoil 104. By reducing the amount of material that would otherwise bedeposited on the coil 104, the generation of particles by the materialwhich is deposited on the coil 104 (and its supporting structures) canbe substantially reduced.

In the illustrated embodiment, the dark space shield 130 is a closedcontinuous ring of titanium (where titanium deposition is occurring inthe chamber 100) or stainless steel having a generally invertedfrusto-conical shape. The dark space shield extends inward toward thecenter of plasma chamber 100 so as to overlap the coil 104 by a distanceof ¼ inch. It is recognized, of course, that the amount of overlap canbe varied depending upon the relative size and placement of the coil andother factors. For example, the overlap may be increased to increase theshielding of the coil 104 from the sputtered material but increasing theoverlap could also further shield the target from the plasma which maybe undesirable in some applications. In an alternative embodiment, thecoil 104 may be placed in a recessed coil chamber (not shown) to furtherprotect the coil and reduce particle deposits on the workpiece.

The chamber shield 106 is generally bowl-shaped and includes a generallycylindrically shaped, vertically oriented wall 140 to which thestandoffs 122 and 124 are attached to insulatively support the coil 104.The shield further has a generally annular-shaped floor wall (not shown)which surrounds the chuck or pedestal 114 which supports the workpiece112 which has an 8″ diameter in the illustrated embodiment. A clamp ring(not shown) may be used to clamp the wafer to the chuck 114 and coverthe gap between the floor wall of the shield 106 and the chuck 114.

The plasma chamber 100 is supported by an adapter ring assembly 152which engages the vacuum chamber. The chamber shield 106 is grounded tothe system ground through the adapter ring assembly 152. The dark spaceshield 130, like the chamber shield 106, is grounded through the adapterring assembly 152.

The target 110 is generally disk-shaped and is also supported by theadapter ring assembly 152. However, the target 110 is negatively biasedand therefore should be insulated from the adapter ring assembly 152which is at ground. Accordingly, seated in a circular channel formed inthe underside of the target 110 is a ceramic insulation ring assembly172 which is also seated in a corresponding channel 174 in the upperside of the target 152. The insulator ring assembly 172 which may bemade of a variety of insulative materials including ceramics spaces thetarget 110 from the adapter ring assembly 152 so that the target 110 maybe adequately negatively biased. The target, adapter and ceramic ringassembly are provided with O-ring sealing surfaces (not shown) toprovide a vacuum tight assembly from the vacuum chamber to the target110.

The coil 104 of the illustrated embodiment is made of ½ by ⅛ inch heavyduty bead blasted solid high-purity (preferably 99.995% pure) titaniumribbon formed into a single turn coil having a diameter of 10-12 inches.However, other highly conductive materials and shapes may be utilizeddepending upon the material being sputtered and other factors. Forexample, the ribbon may be as thin as {fraction (1/16)} inch and exceed2 inches in height. Also, if the material to be sputtered is aluminum,both the target and the coil may be made of high purity aluminum. Inaddition to the ribbon shape illustrated, hollow tubing may be utilized,particularly if water cooling is desired.

Still further, instead of the ribbon shape illustrated, each turn of thecoil, where the coil has multiple turns, may be implemented with a flat,open-ended annular ring such as that illustrated at 200 in FIG. 3. Suchan arrangement is particularly advantageous for multiple turn coils. Theadvantage of a multiple turn coil is that the required current levelscan be substantially reduced for a given RF power level. However,multiple turn coils tend to be more complicated and hence most costlyand difficult to clean as compared to single turn coils. For example, athree turn helical coil of titanium and its associated supportingstructure could be quite expensive. The cost of manufacture of amultiple turn coil can be substantially reduced by utilizing severalsuch flat rings 200 a-200 c to form a multiple turn coil 104′ asillustrated in FIG. 4. Each ring is supported on one side by a supportstandoff 204 a-204 c and a pair of RF feedthrough standoffs 206 a-206 cand 208 a-208 c (FIG. 6) on the other side. As best seen in FIG. 5, thesupport standoffs 204 a-204 c are preferably positioned on the shieldwall 210 in a staggered relationship. Each support standoff 204 a-204 cis received by a corresponding groove 212 (FIG. 3) formed in theunderside of the corresponding coil ring 200 to secure the coil ring inplace.

The cod rings 200 a-200 c are electrically connected together in seriesby RF feedthroughs which pass through the RF feedthrough standoffs 206a-206 c and 208 a-208 c. In the same manner as the support standoffs 204a-204 c, the feedthrough standoffs 206 a-206 c and 208 a-208 c are eachreceived in a corresponding groove 212 (FIG. 3) formed in the undersideof each coil ring adjacent each end of the coil ring. As schematicallyrepresented in FIG. 6, an RF waveguide 220 a external to the shield wallis coupled by the RF feedthrough in feedthrough standoff 206 a to oneend of the lowest coil ring 200 a. The other end of the coil ring 200 ais coupled by the RF feedthrough in feedthrough standoff 208 a toanother external RF waveguide 220 b which is coupled by the RFfeedthrough in feedthrough standoff 206 b to one end of the middle coilring 200 b. The other end of the coil ring 200 b is coupled by the RFfeedthrough in feedthrough standoff 208 b to another external RFwaveguide 220 c which is coupled by the RF feedthrough in feedthroughstandoff 206 c to one end of the top coil ring 200 c. Finally, the otherend of the top coil ring 200 c is coupled by the RF feedthrough infeedthrough standoff 208 c to another external RF waveguide 220 d.Coupled together in this manner, it is seen that the currents throughthe coil rings 200 a-200 c will be directed in the same direction suchthat the magnetic fields generated by the coil rings will constructivelyreinforce each other. Because the coil 104′ is a multiple turn coil, thecurrent handling requirements of the feedthrough supports 206 and 208can be substantially reduced as compared to those of the feedthroughsupports 124 of the single turn coil 104 for a given RF power level.

As previously mentioned, in order to accommodate the coil 104 tofacilitate ionization of the plasma, it has been found beneficial tospace the target 110 from the surface of the workpiece 112. However,this increased spacing between the target and the workpiece canadversely impact the uniformity of the material being deposited from thetarget. As indicated at 250 in FIG. 7, such nonuniformity typicallyexhibits itself as a thickening of the deposited material toward thecenter of the workpiece with a consequent thinning of the depositedmaterial toward the edges of the workpiece. In accordance with onefeature of the present invention, this nonuniformity can be effectivelycompensated by sputtering deposition material not only from the sputtertarget 110 above the workpiece but also from the coil 104 encircling theedges of the workpiece. Because the edges of the workpiece are closer tothe coil 104 than is the center of the workpiece, it has been found thatthe material sputtered from the coil tends to deposit more thicklytoward the edges of the workpiece than the center, as indicated at 252in FIG. 3. This is of course the reverse of the deposition pattern ofmaterial from the target 110. By appropriately adjusting the ratio of RFpower level applied to the coil 104 to the DC power level of the biasapplied to the target, it has been found that the deposition level ofthe material being sputtered from the coil 104 can be selected in such amanner as to compensate substantially for the nonuniformity of thedeposition profile of the material from the target such that the overalldeposition profile of the layer from both sources of sputtered materialas indicated by the deposition profile 254 in FIG. 7 can besubstantially more uniform than that which has often been obtained fromthe target alone. It is preferred that the coil supply sufficientsputtered material such that the material sputtered from the coil bedeposited at a rate of at least 50 Å per minute as measured at the edgeof the wafer in addition to that material being sputtered from thetarget and deposited on the wafer.

It is presently believed that the amount of sputtering which originatesfrom the coil 104 as compared to the sputtering which originates fromthe target 110 is a function of the RF power applied to the coil 104relative to the DC power applied to the target 110. By adjusting theratio of the coil RF power to the target DC power, the relative amountsof material sputtered from the coil 104 and the target 110 may be variedso as to achieve the desired uniformity. As shown in FIG. 8, it isbelieved that a particular ratio of the coil RF power to the target DCpower will achieve the smallest degree (represented as 0%) ofnon-uniformity of the layer of material deposited from both the coil andthe target. As the RF power to the coil is increased relative to the DCpower applied to the target, the deposited layer tends to be more edgethick as represented by the increasingly negative percentage ofnon-uniformity as shown in FIG. 8. (In the sign convention of FIG. 8, anedge thick non-uniformity was chosen to be represented by a negativepercentage of non-uniformity and a center thick non-uniformity waschosen to be represented by a positive percentage of non-uniformity. Thelarger the absolute value of the percentage non-uniformity, the greaterthe degree of non-uniformity (either edge thick or center thick)represented by that percentage. Conversely, by decreasing the ratio ofthe RF power to the coil relative to the DC power applied to the target,the center of the deposited layer tends to grow increasingly thickerrelative to the edges as represented by the increasingly positivepercentage of non-uniformity. Thus, by adjusting the ratio of the RFpower to the coil relative to the DC power biasing the target, thematerial being sputtered from the coil can be increased or decreased asappropriate to effectively compensate for non-uniformity of the materialbeing deposited from the target to achieve a more uniform depositedlayer comprising material from both the target and the coil. For thesingle turn coil 104, a coil RF power to target DC power ratio ofapproximately 1.5 has been found to provide satisfactory results on an 8inch diameter wafer. FIG. 8 depicts the results of varying coil RF powerto target DC power for a three turn coil in which a ratio ofapproximately 0.7 is indicated as being optimal.

It is further believed that the relative amounts of sputtering betweenthe coil and the target may also be a function of the DC biasing of thecoil 104 relative to that of the target 110. This DC biasing of the coil104 may be adjusted in a variety of methods. For example, the matchingnetwork 302 typically includes inductors and capacitors. By varying thecapacitance of one or more capacitors of the matching network, the DCbiasing of the coil 104 might be adjusted to achieve the desired levelof uniformity. In one embodiment, the RF power to the coil and the DCbiasing of the coil 104 may have separate adjustment inputs to achievethe desired results. An alternative power arrangement could include twoRF generators operated at slightly different frequencies. The output ofone generator would be coupled to the coil in the conventional mannerbut the other generator at the slightly different frequency would becapacitively coupled to the coil such that a change in the power levelof the second generator would change the DC bias of the coil. Such anarrangement could provide independent control of the RF power and DCbias applied to the coil. At present, it is believed that relativelylarge changes in DC bias to the coil for a given RF power level would benecessary to have a substantial effect on the amount of materialsputtered from the coil.

Each of the embodiments discussed above utilized a single coil in theplasma chamber. It should be recognized that the present invention isapplicable to plasma chambers having more than one RF powered coil. Forexample, the present invention may be applied to multiple coil chambersfor launching helicon waves of the type described in copendingapplication Ser. No. 08/559,345.

The appropriate RF generators and matching circuits are components wellknown to those skilled in the art. For example, an RF generator such asthe ENI Genesis series which has the capability to “frequency hunt” forthe best frequency match with the matching circuit and antenna issuitable. The frequency of the generator for generating the RF power tothe coil 104 is preferably 2 MHz but it is anticipated that the rangecan vary from, for example, 1 MHz to 100 MHz. An RF power setting of 4.5kW is preferred but a range of 1.5-5 kW is believed to be satisfactory.In some applications, energy may also be transferred to the plasma byapplying AC or DC power to coils and other energy transfer members. A DCpower setting for biasing the target 110 of 3 kW is preferred but arange of 2-5 kW and a pedestal bias voltage of −30 volts DC is believedto be satisfactory for many applications.

In the illustrated embodiment, the shield 106 has a diameter of 13½″ butit is anticipated that good results can be obtained so long as theshield has a diameter sufficient to extend beyond the outer diameter ofthe target, the substrate support and substrate, to shield the chamberfrom the plasma. The shields may be fabricated from a variety ofmaterials including insulative materials such as ceramics or quartz.However, the shield and all metal surfaces likely to be coated with thetarget material are preferably made of the same material as thesputtered target material but may be made of a material such asstainless steel or copper. The material of the structure which will becoated should have a coefficient of thermal expansion which closelymatches that of the material being sputtered to reduce flaking ofsputtered material from the shield or other structure onto the wafer. Inaddition, the material to be coated should have good adhesion to thesputtered material. Thus for example if the deposited material istitanium, the preferred metal of the shields, brackets and otherstructures likely to be coated is bead blasted titanium. Any surfaceswhich are more likely to sputter such as the end caps of the coilsupport and feed through standoffs would preferably be made of the sametype of material as the target such as high purity titanium, forexample. Of course, if the material to be deposited is a material otherthan titanium, the preferred metal is the deposited material, stainlesssteel or copper. Adherence can also be improved by coating thestructures with molybdenum prior to sputtering the target. However, itis preferred that the coil (or any other surface likely to sputter) notbe coated with molybdenum or other materials since the molybdenum cancontaminate the workpiece if sputtered from the coil.

The wafer to target space is preferably about 140 mm but can range fromabout 1.5″ to 8″. For this wafer to target spacing, satisfactorycoverage, i.e., the ratio of aperture bottom deposition thickness tofield deposition thickness, has been achieved with a coil diameter ofabout 11½ inches spaced from the target by a distance of about 2.9inches. It has been found that increasing the diameter of the coil whichmoves the coil away from the workpiece edge has an adverse effect onbottom coverage. On the other hand, decreasing the coil diameter to movethe coil closer to the wafer edge can adversely effect layer uniformity.It is believed that decreasing the coil diameter causes the coil to bemore closely aligned with the target resulting in substantial depositionof material from the target onto the coil which in turn can adverselyeffect the uniformity of material being sputtered from the coil.

Deposition uniformity also appears to be a function of coil spacing fromthe target. As previously mentioned, a spacing of about 2.9 inchesbetween the coil and target has been found satisfactory for a target towafer spacing of 140 mm. Moving the coil vertically either toward oraway from the target (or wafer) can adversely effect deposition layeruniformity.

As set forth above, the relative amounts of material sputtered from thetarget 110 and the coil 104 are a function of the ratio of the RF powerapplied to the coil and the DC power applied to the target. However, itis recognized that in some applications, an RF power level which isoptimum for improving the uniformity of the deposited layer of materialsfrom the coil and the target may not be optimum for generating a plasmadensity for ionization. FIG. 9 illustrates an alternative embodiment ofa plasma chamber 100″ having a coil 104″ formed of a single open endedcoil ring 200 d of the type depicted in FIG. 3. As shown in FIG. 10, thecoil 104″ is coupled through the shield 308 by feedthrough standoffs 206to a matching network 118 and an RF generator 106 in the same manner asthe coils 104 and 104′ described above. However, the chamber 100″ has asecond target 310 which, although generally shaped like a coil, is notcoupled to an RF generator. Instead, the second target 310 formed of aflat closed ring 400 is coupled through feedthrough standoffs 206 to avariable negative DC bias source 312 as shown in FIG. 10. As aconsequence, the chamber has three “targets,” the first and secondtargets 110 and 310, respectively, as well as the RF coil 104″. However,most of the material sputtered from the coil 104″ and the second target310 originates from the DC biased target 310 rather than the RF poweredcoil 104″.

Such an arrangement has a number of advantages. Because most of thematerial sputtered from the coils originates from the second target 310rather than the coil 104″, the relative amounts of material beingsputtered from the coil 104″ and the first and second targets 110 and310 are a function primarily of the relative DC power biasing the target310 and the target 110. Hence the variable DC power sources 111 and 312biasing the first target 110 and the second target 310, respectively,can be set to optimize the uniformity of the deposition of material moreindependently of the RF power setting for the RF generator 106 poweringthe coil 104″. Conversely, the RF power to the coil 104″ can be set moreindependently of the DC biases to the target 110 and the target 310 inorder to optimize plasma density for ionization purposes.

In addition, it is believed that the RF power levels for the coil 104″may be lower as compared to those for the coil 104. For example, asuitable power range for the coil 104″ is 1.5 to 3.5 kW RF. The powerranges for the primary target 110 and the secondary target, i.e., thecoil 310, are 2-5 kW DC and 1-3 kW DC, respectively. Of course, valueswill vary depending upon the particular application.

FIGS. 11 and 12 show yet another alternative embodiment, which includesa multiple turn RF coil and a multiple ring secondary target in whichthe rings of the target are interleaved with the turns of the RF coil.The RF coil of FIG. 12, like the coil 104′ of FIGS. 4-6, is formed offlat rings 200 a-200 c which are electrically connected together inseries by RF feedthroughs which pass through the RF feedthroughstandoffs 206 a-206 c and 208 a-208 c and external waveguides 220 a-220d to the RF source and RF ground.

Interleaved with the coil rings 200 a-200 c of the RF coil are theclosed rings 400 a-400 c of the second target. As schematicallyrepresented in FIGS. 11 and 12, the negatively biasing DC power source312 external to the shield wall is coupled by an external strap 330 a toa DC feedthrough in feedthrough standoff 206 d to the lowest ring 400 aof the second sputtering target. The target ring 400 a is also coupledby the DC feedthrough in feedthrough standoff 206 d to another externalDC strap 330 b which is coupled by the DC feedthrough in feedthroughstandoff 206 e to the middle target ring 400 b. The target ring 400 b isalso coupled by the DC feedthrough in feedthrough standoff 206 e toanother external strap 330 c which is coupled by the DC feedthrough infeedthrough standoff 206 f to the top target ring 400 c of sputteringsecondary target.

Coupled together in this manner, it is seen that the target rings 400a-400 c of the target 310′ will be negatively DC biased so that themajority of the material sputtered from the RF coil and the secondary400 a-400 c target will originate primarily from the target rings 400a-400 c of the secondary target. Because the RF coil is a multiple turncoil, the current handling requirements of the feedthrough supports 206and 208 can be substantially reduced as compared to those of thefeedthrough supports 124 of the single turn coil 104 for a given RFpower level as set forth above. In addition, it is believed that thelife of the sputtering rings can be enhanced as a result of usingmultiple rings. Although the secondary sputtering targets 310 and 400a-400 c have been described as being fabricated from flat rings 400, itshould be appreciated that the sputtering secondary targets may befabricated from ribbon and tubular materials as well as in a variety ofother shapes and sizes including cylinders and segments of cylinders.However, it is preferred that the secondary targets be shaped so as tobe symmetrical about the axis of the substrate and encircle the interiorof the chamber at the periphery of the plasma. The secondary targetmaterial should be a solid, conductive material and may be of the sametype or a different type of conductive material than that of the primarytarget 110. Although the biasing of the primary and secondary targetshas been described as DC biasing, it should be appreciated that in someapplications, AC or RF biasing of one or both of the primary andsecondary targets may be appropriate.

A variety of precursor gases may be utilized to generate the plasmaincluding Ar, H₂ or reactive gases such as NF₃, CF₄ and many others.Various precursor gas pressures are suitable including pressures of0.1-50 mTorr. For ionized PVD, a pressure between 10 and 100 mTorr ispreferred for best ionization of sputtered material.

It will, of course, be understood that modifications of the presentinvention, in its various aspects, will be apparent to those skilled inthe art, some being apparent only after study others being matters ofroutine mechanical and electronic design. Other embodiments are alsopossible, their specific designs depending upon the particularapplication. As such, the scope of the invention should not be limitedby the particular embodiments herein described but should be definedonly by the appended claims and equivalents thereof.

What is claimed is:
 1. An apparatus for use with a signal source, forsputter deposition of a film layer onto a substrate, comprising: avacuum chamber having a substrate support member disposed therein, aplasma generation area within said chamber, and a shield having a wallwhich substantially encircles said plasma generation area and saidsubstrate support member; a first biasable target disposed in saidchamber; a capacitor; and a sputterable coil insulatively carried bysaid shield wall and having a first end coupled to said signal sourceand a second end coupled to said capacitor, wherein said coilsubstantially encircles said plasma generation area and is positioned tocouple energy inductively into said plasma generation area andpositioned adjacent to said substrate support member to sputter materialfrom said coil onto said substrate; further including a first powersupply coupled to said first target and wherein said source includes asecond power supply coupled to said coil.
 2. The apparatus of claim 1wherein said shield is generally cylindrical in shape.
 3. The apparatusof claim 1 wherein said coil is a single turn coil.
 4. The apparatus ofclaim 1 wherein said coil is ribbon-shaped.
 5. The apparatus of claim 1wherein said capacitor maintains a bias on said coil at a levelsufficient to cause said coil to be sputtered in the presence of aplasma.
 6. The apparatus of claim 1, wherein said second power supply isan RF power supply.
 7. The apparatus of claim 6 further comprising athird power supply coupled to said coil.
 8. The apparatus of claim 1,further including a second biasable sputter target disposed between saidfirst biasable target and said substrate support.
 9. The apparatus ofclaim 8, wherein said second sputter target is DC biased.
 10. Theapparatus of claim 9, wherein said second target is negatively biased.11. The apparatus of claim 10, wherein each of said targets is of thesame material.
 12. The apparatus of claim 1 further comprising a secondtarget carried by said chamber spaced from the first target and formedof the same type of material as said first target, said second targetbeing positioned to sputter said second target material onto saidworkpiece so that said coil material, said second target material andsaid first target material are deposited on said workpiece to form alayer.
 13. The apparatus of claim 12 further comprising a biasingcircuit coupled to said second target.
 14. The apparatus of claim 12wherein said coil is formed of the same type of material as said firsttarget, said coil being positioned to sputter said coil material ontosaid workpiece so that said coil material together with said first andsecond target materials are deposited on said workpiece to form a layer.15. The apparatus of claim 12 wherein said second target is a closedring.
 16. The apparatus of claim 12 wherein said second target is acylinder.
 17. The apparatus of claim 12 wherein said signal source is agenerator for applying RF power to said coil, said apparatus furthercomprising: a source for applying a DC bias to said first target; and asource for applying a DC bias to said second target.
 18. The apparatusof claim 12 wherein said coil has a plurality of turns and said secondtarget has a plurality of rings interleaved with the turns of said coil.19. A method of depositing material on a workpiece in a sputterdeposition chamber, comprising sputtering target material onto saidworkpiece from a target positioned in said chamber; sputtering coilmaterial onto said workpiece from a coil having a first end coupled to asignal source and a second end coupled to ground, said coil beinginsulatively carried by a shield wall substantially encircling a plasmageneration area and positioned adjacent to and at least partiallyencircling said workpiece; and inductively coupling energy from saidcoil into said plasma generation area.
 20. The method of claim 19wherein said shield wall is generally cylindrical in shape.
 21. Themethod of claim 19 wherein said coil is a single turn coil.
 22. Themethod of claim 19 wherein said coil is ribbon-shaped.
 23. The method ofclaim 19 wherein said target material sputtering comprises applying DCpower to said target and said coil material sputtering comprisingapplying RF power from said source to said coil.
 24. The method of claim23 wherein said coil material sputtering further comprises applyingpower from another power supply coupled to said coil.
 25. The method ofclaim 19 wherein said target material and said coil material are thesame type of material.
 26. The method of claim 19 wherein said targetmaterial and said coil material are different types of material.
 27. Themethod of claim 19 wherein said target material and said coil materialare sputtered at different rates.
 28. The method of claim 19 furthercomprising sputtering a second target material onto the workpiece from asecond target positioned above the workpiece.
 29. The method of claim 28wherein said first target material sputtering comprises applying DCpower to said first target and said second target material sputteringcomprises applying DC power to said second target.
 30. The method ofclaim 28 wherein said first and second target materials and said firstcoil material are the same type of material.
 31. The method of claim 30wherein said coil is formed of the same type of material as said firstand second target materials, said first coil being positioned to sputtersaid first coil material onto the workpiece so that said first coilmaterial together with said second coil material and said targetmaterial are deposited on the workpiece to form a layer.
 32. The methodof claim 28 wherein said coil has a plurality of turns and said secondtarget comprises a plurality of rings interleaved with turns of saidcoil.